In a typical method of the above type, the toroidal core form of amorphous steel strip, after being built up about the rotating mandrel, is removed from the mandrel and is then formed into a rectangular configuration. When the toroidal core form of amorphous steel strip is removed from the mandrel, it has little ability to resist collapsing in a radially inward direction, especially if it is a large diameter core. Various techniques have been used for preventing such collapse, but these have not been as successful as might be desired. Collapse of the core form can be a serious problem since once the core form has collapsed, it is very time-consuming, and sometimes not even feasible, to restore it to its original configuration. Typically, collapse of the core form will pull apart some or all of the joints in the core form, and if these joints are not restored to their proper sequence, a core failure can occur when the core is subsequently placed in operation.
U.S. Pat. No. 4,972,573--Yamamota et al discloses a core-making method that employs a static mandrel about which strips of amorphous steel are wrapped. This mandrel has an outer periphery that is circular except for a portion of the outer periphery that is formed by a removable section with a flat outer surface. Such a flat outer surface cannot be tolerated in a method such as mine that uses a dynamic mandrel, i.e., a mandrel that rotates as the core form is built up thereon. If the core form built up on a dynamic mandrel has a flattened outer region, this flattened region would cause the rotating mandrel and core form to be out of balance dynamically, thus causing undesirable bouncing around of the mandrel as it is rotated during build-up of the core form. Another disadvantage of employing a mandrel having a flattened outer region in a method that uses a dynamic mandrel and a belt wrapped about the mandrel, i.e., a belt nester, such as I use, is that the flattened outer region interferes with imparting from the belt to the amorphous strips the proper tension as the strips are wrapped about the mandrel.